1. Field of the Invention
The invention relates to nonferrous metallurgy, and more particularly, to pyrometallurgical methods and furnaces for processing heavy nonferrous metal raw materials.
The present invention is particularly suitable for extracting copper, nickel, lead, zinc from monometallic and polymetallic raw materials.
2. Description of the Prior Art
In a pyrometallurgical processing of heavy nonferrous metal raw materials, the oxidation of said materials gives off a substantial amount of heat, which, when using oxygen-enriched air or pure oxygen, is sufficient to cover the requirements of the process. However, the oxidation of a molten sulfide, e.g., a matte, by a gas containing more than 30% oxygen leads to a considerable local overheating of the zone where the gas is injected into the melt and results in damage to said section of a metallurgical apparatus.
At present, there are being developed and introduced industrially a number of methods for processing heavy nonferrous metal sulfide raw materials involving a maximum utilization of the heat from the oxidation of said sulfides.
By their main characteristics, said methods may be classed with three trends having some variations.
One of said technological trends in the development of sulfide raw materials processing consists in injecting heavy nonferrous metal raw materials in the form of a dry flotation concentrate by means of oxygen or a gas enriched with oxygen into the gas space of a smelting unit and oxidizing said materials without direct contact with walls of said unit. In this case, there evolves a great amount of heat and the off gases are high in SO.sub.2.
However, as each particle of the raw materials is oxidized individually in a jet of oxygen-bearing gas, a high proportion of nonferrous metals turns to oxides and dissolves in slag. In subsequent processing of said slag, the dissolved nonferrous metals precipitate therefrom as very fine inclusions which are very difficult to separate from the slag, this greatly lowering the effectiveness of the process as a whole.
Another trend in the processing of sulfide raw materials with the aid of oxygen-bearing gas of high oxygen content is to supply said gas through top tuyeres upon the surface of the melt. This results in an increased service life of the smelting unit, but requires a complicated tuyere design, a high-pressure gas for stirring the melt, involves a rapid failure of tuyere tips. In addition, the slag, being a lighter product, floats on the surface of the melt and shields the sulfides and is the first to be overoxidized, said inconvenience leading to greater losses of nonferrous metals with the slag.
Still another trend consists in injecting an oxygen-bearing gas through side tuyeres into a layer of molten matte similarly to a known process, such as converting, and feeding a charge into a stirred body of melt. However, as already noted, in areas where a gas with more than 30% is injected, the melt and the enclosing walls of the smelting unit tend to overheat with resultant damage to said walls. Therefore, use is made only of air enriched with oxygen to less than 30%. This impairs thermal conditions, lessens the content of SO.sub.2 in the off gases and lowers overall efficiency. The injection of an oxygen-bearing gas into matte also increases the oxidation of nonferrous metals and contributes to their greater losses with the slag.
There are various combinations of the above technological variants, but their effect as regards the improvement in the potentialities of the processes is slight.
The closest to the present invention is the continuous smelting and converting of copper mattes (see U.S. Pat. No. 3,832,163, Cl.75-74 H/c22b 15/00).
The process is effected in a reactor divided into three zones along a horizontal axis: a smelting and converting zone, a copper accumulation zone and a slagging zone. A copper concentrate is mixed with a flux and a concentrate from slag-treatment, the resultant mixture is pelletized, and the pellets are continuously or intermittently charged into a reactor upon the surface of a melt. At the same time, air or air enriched with oxygen is injected into the lower part of the matte layer at a velocity ensuring an intensive stirring of the melt in said zone and a continuous and effective oxidation of iron and sulfur contained in the concentrates. The temperature in the smelting and converting zone is maintained at a value exceeding the melting points of metal copper, of matte and of slag, with the effect all of the phases in the reactor are in a molten state. The reduced metal copper is collected in its accumulation zone, whence it is tapped at required intervals. Molten slag accumulates in the slagging zone, whence it is also intermittently or continuously removed. Air and a reducing gas are injected into the slagging zone. A solid reducing agent or a portion of the copper concentrate of the charge may also be injected into the slag. The slag discharged from the reactor is slowly cooled, ground, flotated, and the flotation concentrated is mixed with the starting copper concentrate and flux prior to pelletizing.
As, in the above smelting method, an oxygen-bearing gas is injected into the matte layer, the gas is but little enriched with oxygen. This results in considerable losses of heat with the off gases and necessitates the burning of a large amount of carbonaceous fuel, or as much as 3.95.10.sup.6 kcal/ton of dry concentrate. In addition, the injection of the whole of the oxygen-bearing gas into the body of matte leads to a considerable increase in the amount of oxidized nonferrous metals, the oxides passing to slag, a phenomenon well known from converting practice. And although the method under consideration provides for special procedures for reducing the slag prior to tis discharge, the content of copper in the slag is not lower than 8 or 10%. Thus, the direct recovery of copper to crude metal is a mere 50-60%, and the resultant slag requires flotation denudation. Because of the lack of conditions for an effective separation of matte from slag and because of the stirring of slag and of matte in an oxidizing atmosphere, a direct recovery of about 50% of copper necessitates in said method the holding of the melt in the furnace for a long time, this bringing down the specific efficiency of the unit per square meter of horizontal section of the furnace to 10 t/m.sup.2.24 h or to 0.42 t/m.sup.2.h.
Thus, no conditions are provided in the above method for an effective processing of sulfide materials with the use of oxygen-enriched gas.
Among the known apparatus for processing heavy nonferrous metal raw materials, the closest to the present invention is a modified fuming furnace (see U.S. Pat. No. 3,892,559 of July 1, 1975, U.S.Cl. 75/21) which is essentially a rectangular shaft composed totally of steel water-cooled water jackets. Side tuyeres for injecting a gas into the melt are placed near the hearth, this resulting practically in an oxygen-bearing gas being injected into the matte layer. The devices employed to feed the charge into the melt are modified tuyeres provided with additional sleeves, one each. Slag, matte and crude metal are discharged at required intervals through a taphole without being separated inside the furnace shaft, whereas the gaseous smelting products are exhausted with the aid of a flue arranged in the top part of the shaft.
The above apparatus fails to provide an effective separation of the slag from the matte or crude metal inside the furnace and their individual discharge because of a low arrangement of the tuyeres and the stirring of the whole of the molten mass inside the furnace shaft. Steel water jackets in the tuyere zone and the stirring of the melt with a high matte content make it impossible to raise the efficiency of the smelting unit through the use of a blast with a high oxygen content for fear of melting off the slag lining the water jackets and damaging the walls thereof in case of inadequate heat removal. A substantial disadvantage of said apparatus is a lack of continuous separate discharges of slag and matte.
All this results in a slag with a high residual content of nonferrous metals and, therefore, in a poor economic performance of the process.